The Western Star

CINDY DAY: A spike in the weather

Sunlight appears to come to us in rays, although what we’re really seeing is sunlight scattering off of particles in the atmosphere. This lovely example of diffraction spikes was submitted by Stephen Matheson, Cape Wolfe, P.E.I.- Contributed

I grew up in a Catholic household. Following my first communion, I was given a small card to keep by my bedside and later in my purse. It was a prayer card. The photo on the front was breathtaking: beams of sunlight radiating through ominous clouds. I came across that tiny card the other day. (It’s back in my purse — it can’t hurt.)

To be honest it felt a little strange, looking at it now, knowing more about the science behind the rays.

The rays are called diffraction spikes. They are lines that radiate from a bright light source in photographs; they make many late day sunsets appear quite heavenly. Where do these broad streaks or spikes of light come from?

Under most circumstances, sunlight actually does appear to come to us in rays, although what we’re really seeing is sunlight scattering off of particles in the atmosphere.

The reason the sun can appear to have rays in photographs is that the edges of the lenses and the hardware holding them in place can cause light to bend around obstacles and interfere with itself in a pattern that reflects the shape of the optic or whatever is holding it.

But we also see those rays with the naked eye. The sun can appear to have rays even when you’re not looking through a lens because your eye is an optic too. Your eye has a lens whose curvature and diameter are controlled by the muscles in your iris. The edges of the iris are pretty rough. That causes some diffraction.

The same applies to stars. If I asked you to draw a star, I bet it would have points. Real stars, the ones in space, are round. Again, the diffraction spikes are created when light passes through a reflecting telescope. It results in what looks like rays shooting out from the centre.

Another theory describes how eyelashes can act like the supporting structure of a telescope by blocking light. Squint your eyes at a streetlight at night, and you’ll see some vertical lines.